The present invention relates to a vehicle control apparatus for conducting driving, steering and braking of a vehicle through electronic control.
Electronic control for vehicles have recently expand rapidly aiming at reduction in fuel consumption and exhaust gas and improvement on safety. Controllers are used in a vehicle for controlling an engine, a transmission, a brake and steering, and in addition an air bag, doors, mirrors and the like. A vehicle is equipped with a number of controllers. Basically, these controllers detect the states of control targets from various sensors and instruction information on a drive from operation switches, and in accordance with the state information and instruction information, control actuators such as electromagnetic valves and motors. A signal output from each sensor includes an analog signal and a pulse signal. Controllers are therefore equipped with an A/D converter for converting an analog signal voltage into a digital value and a timer to be used for converting a period or the like of a pulse signal into a digital value. Since actuators such as electromagnetic valves and motors are controlled by pulse signals such as PWM pulse signals, controllers are equipped with a timer to be used for outputting a pulse signal. Controllers are further equipped with a general I/O port for digital signal inputs/outputs in order to fetch information on operation switches and perform simple ON/OFF control for electromagnetic valves. A general controller uses a microcontroller having a central processor unit (CPU), a memory, A/D converters, timers, general I/O ports and the like respectively integrated on the same chip. The advantages of using a microcontroller are mainly reduction in the number of components and corresponding feasibility of substrate designs. However, the A/D converter, timer, general I/O port and the like have each a number of pins to allow a plurality of signals to be connected. There arises therefore an issue that the chip size and package of a microcontroller cannot be made small even if a chip integration degree is improved by advancement of micro patterning.
To address this issue, a method has been proposed which reduces the number of pins of a microcontroller by connecting the microcontroller, A/D converters and driver ICes through serial communications (refer to “New Serial Microcontroller Links—Micro-Link-Interface And Micro-Second-Channel”, SAE-2003-01-0112). According to this method, a driver IC is equipped with a unit for generating a plurality of PWM pulse signals for driving actuators, and ON/OFF commands for the PWM pulse signals generated by using a timer in the microcontroller are transmitted through serial communications to the driver IC which in turn generates the PWM pulse signals.